The correct answer is to add a default route (::/0) in the private subnet's route table pointing to the egress-only internet gateway. This works because an egress-only internet gateway is a horizontally scaled, highly available AWS component that enables outbound-only IPv6 communication from instances in a VPC, but it does not allow any inbound traffic initiated from the internet. Unlike a NAT gateway for IPv4, the egress-only gateway does not require an IPv6 address assignment; instead, it simply acts as a next-hop target for the default IPv6 route, allowing private instances to reach the internet while remaining unreachable from outside. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this concept tests your understanding of IPv6 routing and the distinction between outbound-only and bidirectional gateways. A common trap is confusing the egress-only gateway with a NAT device or assuming route propagation is needed, but the key is that the gateway itself is stateless and the route table entry is all that is required. Memory tip: think “Egress = Exit only, ::/0 points out, no inbound allowed.”
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company has a VPC with an IPv6 CIDR block and wants to provide internet access to instances in a private subnet using an egress-only internet gateway. Which of the following must be configured correctly?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add a default route (::/0) in the private subnet's route table pointing to the egress-only internet gateway.
Option C is correct because an egress-only internet gateway is used for IPv6 outbound-only internet access, and the private subnet's route table must have a default route (::/0) pointing to the egress-only internet gateway. Option A is incorrect because IPv6 addresses are not assigned to the egress-only internet gateway. Option B is incorrect because NAT64 is not required. Option D is incorrect because the egress-only internet gateway does not use route propagation.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Configure NAT64 on the VPC to translate IPv6 to IPv4.
Why it's wrong here
NAT64 is for IPv6 to IPv4 translation, not needed for native IPv6 access.
✗
Enable route propagation for the egress-only internet gateway in the route table.
Why it's wrong here
Route propagation does not apply to egress-only internet gateways; routes are static.
✓
Add a default route (::/0) in the private subnet's route table pointing to the egress-only internet gateway.
Why this is correct
This allows IPv6 traffic from the private subnet to reach the internet outbound.
Assign an IPv6 address to the egress-only internet gateway.
Why it's wrong here
Egress-only internet gateways do not have IPv6 addresses; they are virtual devices.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Network Implementation — This question tests Network Implementation — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Add a default route (::/0) in the private subnet's route table pointing to the egress-only internet gateway. — Option C is correct because an egress-only internet gateway is used for IPv6 outbound-only internet access, and the private subnet's route table must have a default route (::/0) pointing to the egress-only internet gateway. Option A is incorrect because IPv6 addresses are not assigned to the egress-only internet gateway. Option B is incorrect because NAT64 is not required. Option D is incorrect because the egress-only internet gateway does not use route propagation.
What should I do if I get this ANS-C01 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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